Television amplifier



DH; 31, 1940. sc sm 2,227,914-

TELEVISION AMPLIFIER Filed Dec. 11. 1956 Jnrenfor:

particularity in the appended claims.

Patented Dec. 31, 1940 PATENT (OFFICE TELEVISION AMPLIFIER Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application December 11, 1936, Serial No. 115,385 i In Germany December 17, 1935 2 Claims. (Cl. 179-171) The present invention relates to amplifiers and especially to amplifiers suitable for use in amplifying picture signals in television systems.

It is known that the limit in respect of the frequency range which is to be transmitted by a resistance-capacity coupled amplifier for image transmission purposes should besitua'ted below the frame frequency. This amounts for trans missions with continuous scanning to 25 cycles and to. those in which scanning is performed in groups of lines to 50 cycles. The frequency limit in these cases must amount to approximately 10-20 cycles. In the case of amplifiers which are designed forlow frequencies of this nature it can be observed that ripples in the mains voltage which feeds the anodecircuits of the amplifier are also amplified to a considerable extent and cause strong fluctuations in the light intensity of the image at the receiving end.

An object of the invention is to prevent fluctuations inthe potential of the power supply having any appreciable effect on the reproduced picture without reducing the amplification of the low frequencies.

According to the invention, in a resistancecapacity coupled multistage electrical amplifier with filter units associated with the individual amplifier stages for eliminating fluctuations in the output potential which would otherwise appear as a result of fluctuations in the potential of the power supply, the filter units are so dimensioned that the time constant of the filter unit in the anode circuit of each valve is inversely proportional to the time constant of the coupling unit in the gridcircuit of that valve, the amplification given to the fluctuating component by each valve being so adjusted that it compensates for the decrease of potential amplitude of the fluctuating component along the coupling path to the grid of the valve in question.

The novel features which I believe to be charac'teristic for my invention are set forth with My invention, however, both as to its organization and method of operation together with further objects and advantages thereof may be best understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 shows an exemplary connection arrangement according to the invention, while Fig. 2 represents a vector diagram for use in explaining the invention.

Figure 1 shows a multi-stage resistance-capacity coupled thermionic valve amplifier comprising valves i, la lb with anode resistancesZ, 2a and 21); grid coupling condensers 3 and 3a; and grid leak resistances 4 and 4a. In addition, the amplifier comprises filter units 5, 6; 5a, 6a.; 5b, 6b, of which 5, 5a. and 5b are resistances and 6, 6a, and 6b are earthing condensers. The. amplifier is fed with power from a power supply unit 1 the output potential of which is likelyto fluctuate due to fluctuations in the voltage of the public electric supply mains to which it is connected. The electrieal dimensions of the filter units 511., 6a, etc. and the coupling units 3, 4, etc. are chosen to satisfy certain conditions which will be explained later and thereupon prevent any fluctuations in power feed from unit I from having any disturbing effect on the amplified output from valve l.

In Figure 2, l (the line ac) is a vector representing the alternating or fluctuating component of the current source 1 shown in Figure 1. The potential supplied to the last amplifier stage comprising valve I and arriving at point P is smoothed by the filter unit 5a, 6a. The fluctuating component 1' flowing through the filter unit 5a, 6a produces potentialdrops 5 and'B at the resistance 5a and at the condenser 6a respectively. The potential drop 6' at condenser 6a is applied via resistance 2a to the anode of valve la and is also applied to the succeeding valve I via the potential divider comprising condenser 3' and grid leak resistance 4. With a suitable dimensioning of the circuit elements the potential decrease of the fluctuating component across re-f sistance 4, which is shown in Figure 2 by the vector 4' (the line we), will be in phase with the vector 1', whilst the potential drop of the fluctuating component across condenser 3, which is inindicated by 3 (the line eb) in Figure 2, will be displaced by 90 with reference to 1. It is added that in the above consideration the potential drop across the element 2a is neglected.

In Figure 2, the triangles abc and abe are similar to one another because they both have two angles, namely a right angle and angle cab, and one line (ab) in common, and one thus obtains the following equation:

which also holds good for the magnitudes of the corresponding circuit elements 5a, 6a, 3, 4. It

therefore follows that the time constant of the filter unit 5, 6 must be inversely proportional to the time constant of the coupling unit 3, 4, i. e. the product of the values of the resistances 4 and 5a must be equal to the product of the impedances of the condensers 3and So. If this latter condition is observed at each stage then the fluctuating component at the grid of each valve will be in phase with the fluctuating component at the anode of that valve. The valve itself effects a reversal of phase and at the same time amplifies the fluctuating component, the :anode load being constituted by the filter unit 5a, 6a etc. belonging to the valve in question. The degree of amplification given by each valve is so adjusted that the amplified fluctuating component neutralizes the fluctuating component ape plied to the anode circuit 1. e. the vector ad is made equal to the vector we; in other Words, the degree of amplification given by each valve to the fluctuating component is so adjusted as to compensate exactly for the potential decrease of the f fluctuating component along the coupling path leading to the grid of the valve in question. The a.

Value of the filter resistance 5a is chosen by experiment to satisfy the above condition and the value of the corresponding .filter condenser 6a is then determined from the condition that the time constant of 5a, 6a must be the reciprocal of the time constant of 3, .4.

It isto be observed that if the frequency of the ripple potential varies, the phase shifts in Fig. 2 would also vary,-but that the resulting phase position and also the drop in potential remain constant, since with an increase of the ripple frequency the ripple potential of P in Fig. 1 decreases. The coupling factor to the grid of the next tube-is improved, so that the grid interfering potential ismore liable to be constant and the amplifying condition 2 is also fulfilled in the case of diiferent frequencies. If on the other hand the ripple potential assumes a higher frequency, it is steadied to a better extent in the filter circuits by condenser 6, so that the arrangement in no way exhibits interferences to any appreciable degree. The applicant has found that amplifiers according to the invention operate satisfactory exactly in the case of interfering mains poten-' tials of more than 5% of the nominal value, caused by a Tirril regulator actuated once every second. The output potential was remarkably constant.

I claim: 7 1. A television amplifier comprising a plurality of resistance-capacity coupled stages of amplification, each of said stages of amplification including a discharge tube having a cathode, a control electrode and an anode, a source of potential having positive and negative terminals, means including a load impedance and a filter resistance connected in series between the anode of one of the tubes and the positive terminal of the source of potential to maintain the anode positive with respect to its associated cathode, a filter condenser connected between the negative terminal of the source of potential and the junction of the load impedance and the filter resistance, a coupling condenser for connecting the anode of the one tube to the control electrode of the next succeeding tube, and a grid resistance connected between the control electrode of said last-named tube and the negative terminal of the source of potential, .theproduct of the values of the filter and grid resistances being substantially equal to the product of the impedances of the filter and coupling condensers whereby substantially complete compensation for variations in the intensity of the source of potential will result.

2. A television amplifier comprising a plurality of stages of amplification, each including a discharge tube having a cathode, a control grid and an anode, a source of potential having positive and negative terminals, means including a series connected load resistance and filter resistance connected between the anode of one of the tubes and thepositive terminal of the source of potential to maintain the anode positive with respect to its associated cathode, a filter condenser connected between the cathode and the junction of the load resistance and the filter resistance, a coupling condenser for connecting the anode of the one tube to the control grid of the next succeeding tube, a grid resistance coupled between the control grid and the cathode of said lastmentioned tube, and means including a second load resistance and said source of potential for maintaining the anode of said last-mentioned tube positive with respect to its associated cathode, the time constant of the filter resistance and filter condenser being inversely proportional to the time constant of the grid resistance and coupling, condenser whereby fluctuations in the intensity of the source of potential will be substantially alleviated; i

KURT SCHLESINGER. 

